I'm writing about this because I didn't find one place online that explained all this stuff at once.
I bought my wife a few Game and Watch games for Christmas this year, and one of them was sight unseen--the seller didn't have the batteries or urge to test it, but it seemed in good shape.
When I put batteries in it, though, I couldn't see the screen. At first, I thought it was completely dead, but it made sound. When I looked closer, I could make out really faint figures moving on the screens.
This meant the polarized film over the screen was toast. Super easy fix. If you have a Game and Watch with a fading LCD, here's what to do: get something polarized (like sunglasses) and place it over the screen. You might have to rotate it a little, and you should see the screen go black on one of the angles. Rotate another 90 degrees and you should have a normal looking screen with DK Jr. bopping around on it.
Here's the lower screen with the old and new polarized film.
I bought a pack of 10 sheets of polarized film on Amazon. They're a bit thicker than the originals, and as you can see by the photo above, I had to use them diamond-shaped to get the angle right. I figured I had to trim them anyway, so I was fine with that.
The Game and Watch screens have a few elements to them. From the very front layer to the back, you'll have the polarized film, one or two scenery panels (make sure you keep track of which end is up), the actual glass LCD panel, and behind that, a silver plate. More on that plate later.
Open up the game. Be careful, these things are old and the plastic might be brittle. You don't want to snap off a screw post. There are other walkthroughs online for how to disassemble these, but they are super simple, so you can probably figure it out. Do one side at a time. I did the upper screen first, since I didn't want to deal with the buttons. Behind the upper screen is a hefty metal plate to keep everything in place. You have to unscrew that and (gently) lift it off to get at the screen proper.
Here's the new, untrimmed film next to the old, yellowed film.
Use the old film as a template and cut out the shape. It's okay to cut a little big, you can always trim it to fit. Notice the pattern of notches at the corners of the film--it'll help you orient it properly when you reassemble (I think the one in the photo is upside-down).
Button pads like to fall out. Watch out for the metal bits--they disappear quickly.
In the photo above, you can see how everything's laid out. I opened it with the button console down (in 'closed' position). The LCD still has the silver backing behind it, and there's a second scenery panel between the silver backing and the glass LCD. Then, still in the button console, the foreground scene panel is on top of the polarized film.
That polarized film also serves as a sort of screen protector. It's the cheapest, most replaceable part of the screen, so if it gets faded or scratched, it's not a big deal to repair.
Pop out the scenery panel and the old polarized film, and throw your new polarized film in place. Be careful--the polarized film will have a thin layer of protective plastic over one or both sides. Peel off that protective plastic before you install the film in the game.
Then carefully sandwich the game together (I had a devil of a time with this--the layers of plastic kept sliding around, so sometimes a scenery panel stuck out too far, or the polarized film popped out and got in the way. Just be patient, keep everything lined up, and fit the screen and button console together.
Once they're together, hold them that way and take a look at the screen. In mine, the front scenery panel kept sliding up, exposing way too much of the black border. If the panels look pretty centered, screw the game back together.
And now you can see Junior.
Remember the silver plate behind the screens? Not the hefty one keeping the top screen in place, but the little one behind the LCD that makes the screen look silvery. That's also replaceable. If you have a Game and Watch with a circular stain behind the screen that almost looks burnt, that's a good indication that moisture got into the game at one point and now the silver plate is tarnished.
You can buy replacement silver plates for about $4 plus shipping from a guy in Spain who sells Game and Watch repair parts on eBay. I got a few to fix an Oil Panic game.
Here's what the lower screen looked like on the Oil Panic game:
Here's the upper screen--not as bad, but almost as faded as the Donkey King II game:
I swapped out the silver plate on the lower screen, as well as both polarized films. Now it looks like this:
Not too bad! Of course, with the silver plate replaced in the lower screen, the upper screen looks dingy by comparison. I'll have to open it up again and replace that one.
Look closer at the lower screen.
I'm a little peeved at these blotches (nobody's fault, just annoying). This is one of the things you just can't fix: screen bleed. This game isn't bleeding too badly, and if I keep it relatively climate-controlled, it shouldn't get much worse. But knowing I can't fix it is a little galling.
Thankfully, this is a wicked little game, so I never really have time to notice these blotches while I'm actually playing. I'm too busy yelling at the little guy for never being where I need him to be when I have to empty my bucket.
Well, that's that. I hope this writeup was helpful and/or enlightening. These Game and Watch games are really well made, easy to maintain, and a lot of fun to play. If you have a broken one sitting in a drawer, take a closer look. You might be able fix it up with a few bucks and around 30 minutes.